Abstract: Two signal electrodes and a reference electrode are attached to dielectric members, from which their front faces project for engaging a person's skin. Embedded in the dielectric members that enclose the two signal electrodes are electrostatic shields that are behind the electrodes and spaced from them. There are electrical conductors for connecting the signal electrodes to the differential amplifier of a heart rate monitor, and other electrical conductors for connecting the shields and the reference electrode to the common input terminal of the amplifier.